The present invention generally relates to detecting a collision between a movable component of an imaging system and an object. In particular, the present invention relates to object collision detection using a Proportional Integral Derivative (PID) controller on a motorized, mobile C-Arm.
Medical diagnostic imaging systems encompass a variety of imaging modalities, such as x-ray systems, computerized tomography (CT) systems, ultrasound systems, electron beam tomography (EBT) systems, magnetic resonance (MR) systems, and the like. Medical diagnostic imaging systems generate images of an object, such as a patient, for example, through exposure to an energy source, such as x-rays passing through a patient, for example. The generated images may be used for many purposes. For instance, internal defects in an object may be detected. Additionally, changes in internal structure or alignment may be determined. Fluid flow within an object may also be represented. Furthermore, the image may show the presence or absence of objects in an object. The information gained from medical diagnostic imaging has applications in many fields, including medicine and manufacturing.
Radiation imagers, such as x-ray machines, are typically accurately positioned close to a patient or object to be imaged in order to provide desired imaging information. One type of radiation imager is a mobile C-arm system. In the medical field, the mobile C-arm system may be used for general surgery, orthopedic procedures, pain management procedures, vascular procedures, and cardiac procedures, for example. Typically, the mobile C-arm has an x-ray source mounted at one end of a mainframe and a detector, such as an image intensifier, mounted at the other end of the mainframe. The mobile C-arm may be moved in relation to the object, such as a patient, to be imaged.
Motorized motion of any of the axes of a mobile C-arm system poses possible risks to the patient and to the imaging system and other equipment. It is desirable to prevent or minimize collisions between the mobile C-arm and an object, such as the patient. A possibility of collision exists whether the C-arm is moved through automated trajectory tracking or through direct user input from a user interface device. It is therefore desirable to prevent or minimize collisions when the mobile C-arm is controlled by both an external user and by an automated system or program. A method and system for minimizing collisions that do occur would also be highly desirable.
Imaging systems typically use one of two types of anti-collision sensors: contact sensors and proximity sensors. A proximity sensor detects the presence of an object within a given distance from a movable part of the C-arm imaging apparatus. A proximity sensor may be a capacitive proximity sensor. Current proximity sensors are limited by the complexity of electronic circuitry. Complex, additional electrical circuitry impacts the cost, maintenance, and performance, for example, of the imaging system. Current sensor systems are also limited by distances between sensors and imaging system components. That is, operating constraints limit the distance between a proximity sensor and an image intensifier, for example. Furthermore, capacitive proximity sensing has not been used with a mobile C-arm apparatus.
Another type of collision sensor is a contact sensor. A contact sensor may use a bumper, for example. The contact sensor detects a change in a signal resulting when the bumper contacts an object. Typically, the contact sensor detects a change in pressure from contact with the object.
However, current systems may misinterpret a collision as an error in system performance. Misinterpretation may result in more power being applied to motors in the motorized C-arm system. Eventually, the system may apply the maximum power available and, thus, apply maximum torque to the system. High torque may result in unacceptably high forces exerted on the collided object.
Thus, a need exists for an improved method and system for object collision detection on a motorized, mobile C-arm system.